Experimental Results For Various Conditions Research Articles

Efficient Nonlinear Precoding for Massive MIMO Downlink Systems With 1-Bit DACs

The power consumption of digital-to-analog converters (DACs) constitutes a significant proportion of the total power consumption in a massive multiuser multiple-input multiple-output (MU-MIMO) base station (BS). Using 1-bit DACs can significantly reduce the power consumption. This paper addresses the precoding problem for the massive narrow-band MU-MIMO downlink system equipped with 1-bit DACs at each BS. In such a system, the precoding problem plays a central role as the precoded symbols are affected by extra distortion introduced by 1-bit DACs. In this paper, we develop a highly efficient nonlinear precoding algorithm based on the alternative direction method framework. Unlike the classic algorithms, such as the semidefinite relaxation (SDR) and squared-infinity norm Douglas-Rachford splitting (SQUID) algorithms, which solve convex relaxed versions of the original precoding problem, the new algorithm solves the original nonconvex problem directly. The new algorithm is guaranteed to globally converge under some mild conditions. A sufficient condition for its convergence has been derived. The experimental results in various conditions demonstrated that the new algorithm can achieve the state-of-the-art performance comparable with the SDR algorithm while being much more efficient (e.g., more than 300 times faster than the SDR algorithm).

Pull-Out Behaviour of Square Anchor Plates in Reinforced Soft Clay

Anchor plates are generally used for structures like transmission towers, mooring systems, etc. where the uplift and lateral forces are expected to be predominant. The capacity of anchor plate can be increased by increasing the size of the plate, depth of embedment and grouping of anchors. However due to space constraints, it was found that use of geosynthetic can be beneficial in increasing the uplift capacity without altering size of plates. Most of the past research in this area focused on the response of plate anchors in cohesionless type of soil. In the present study it was aimed to determine the uplift capacity of the anchor plates in cohesive type of soils with geosynthetic reinforcement. Numerical simulations were carried out on three different sizes of square anchor plates using general-purpose finite element software ABAQUS. Material non-linearity was considered in the analysis using hypoelastic model. For reinforcement, a single layer geosynthetic was placed at three different positions from the plate. The effects of various parameters such as, embedment ratio, position of reinforcement and width of reinforcement has been studied. Results obtained from the numerical analysis were compared with the previously published experimental results for various conditions. It was also observed that the inclusion of reinforcement results in a shift in overall failure behaviour of plate anchors. Parametric study involving the embedment depth, position of reinforcement in embedded soil indicates the significant role in the behaviour of anchor plates in reinforced soil in terms of ultimate pull-out capacity. The uplift capacity was expressed in terms of dimensionless breakout factor. A formulation for breakout factor has been proposed for different embedment ratio of anchors in reinforced soils.

Analytical and experimental analysis of the formability of copper-stainless-steel 304L clad metal sheets in deep drawing

The formability of the clad metal sheets is influenced by many factors such as mechanical properties of the component metals, so that producing clad cups with high formability free of defects is not easily possible. The behavior of clad sheet, vis-a-vis single-layer sheets, is comprehensively studied through experimental as well as numerical methods using the finite element analysis. In this study, the limiting draw ratio and thickness variations of copper-stainless-steel 304L clad metal sheet have been investigated. Finite element simulations were conducted to study the process and to predict the fracture position. The experimental results in various conditions were compared and the desirable state was recognized. Results illustrated that the thickness distribution of stronger material (stainless-steel 304L) was somewhat more uniform than the weaker one (copper layer). It is demonstrated that the strain distributions in the deep-drawn cups obtained by the FE method can be used to predict the location of fracture in the experimental tests. Furthermore, it was found that the formability of clad sheets, in different layout settings, with respect to various parameters, followed the same trends as single-layer sheets.

Numerical investigation of nucleate boiling heat transfer on thin substrates

The objective of this paper is to define the guidelines for the design of new boiling test sections with a large number of artificial nucleation sites during nucleate boiling for thin substrates horizontally immersed in a saturated liquid with artificial cavities located on the upper surface. The findings of numerical simulations of pool boiling heat transfer for a single bubble and for a large number of nucleation sites based on the analysis of experimental cases were analysed. Dedicated test sections were used in experiments for the study of boiling mechanisms and interactions between active sites so that the numerical models representing the physics of the problem could be improved. The hybrid nature of the code used in this study, combining the complete solution of the three-dimensional time-dependent energy equation in the solid substrate with semi-empirical models representing the physical phenomena occurring in the liquid side, in a simplified way, allows a large number of simulations in a reasonable computational time.The present paper focuses in the first part on the capability of the model to reproduce the experimental results for various conditions, while in the second part, the results for a large number of nucleation sites are analysed. Regarding the single bubble growth, two series of simulations will be presented in this paper: the first one analyses the mechanisms of nucleate boiling on a silicon substrate immersed in the dielectric fluid FC-72. The second series studies the behaviour of bubbles on metallic substrates, platinum and titanium, in saturated water. In the last section, the effect of the position of a site during simulations of a large population of sites (of the order of 100) on the waiting time, growth time, type and occurrence of coalescence and the thermal characteristics is presented.

EXPERIMENTAL STUDY ON THE DISCHARGE CHARACTERISTICS OF SLUICE FOR TIDAL POWER PLANT

The discharge characteristics of sluice caisson for tidal power plant were investigated by carrying out a physical experiment in a planar open channel. The experiment was performed by installing 10 sluice models whose scale was 1/70 of the prototype in the planar open channel, where apron sections were made in front of and behind the sluice models to reproduce the field condition. The locations and method of measuring water levels were carefully determined so as to accurately estimate the discharge coefficient, an index of representing the discharge performance of the sluice caisson. The experimental results for various conditions of flow rates and water levels showed that the discharge coefficient of the sluice caisson was in the range of 1.3 to 1.47. These values were substantially smaller than those obtained from the previous study performed in a two-dimensional open channel (Lee et al., 2010). As the previous study had some limitations in reproducing the bathymetric and flow conditions in the field, it is more recommended to use the results acquired in the present experiment.

Estimation of tyre-road friction coefficient

Tyre-road friction coefficient is hard to detect while it is important for vehicle control systems, especially the vehicle active safety control systems. This paper presents a maximum aligning moment method which requires no additional sensors if the vehicle is equipped with an electric power steering (EPS) system. A non-linear observer method is designed for the estimation of friction coefficient as well as the continual estimation of tyre slip angles. One combined estimation method is proposed to compensate for the drawbacks of the two methods above. These estimation methods are verified by computer simulations with experimental results in various conditions.

조력발전용 수문 성능평가를 위한 평면 수리모형실험

The discharge coefficient and spatial velocity distribution were clarified by carrying out a physical experiment to assess the performance of sluice for tidal power generation. The physical experiment was performed by manufacturing 10 sluce models whose scale is 1/70 of the prototype and installing it in the planar open channel, which has apron sections in front of and behind the sluice models. In particular, it was attempted to reasonably determine the locations and method of measuring water levels that may affect estimation of the discharge coefficient. Based on the experimental results for various conditions of discharges and tidal levels, the discharge coefficient of the sluice in the experiment was estimated as 1.3 to 1.4. Meanwhile, it was found that velocities were 2~3% faster at the sluices near the central region whereas 4~5% slower at the sluices on both sides, in comparison to the average value of the mean velocities of the ten sluices.

Composition change of stainless steel during microjoining with short laser pulse

Weld metal composition change in 200μm deep, 304 stainless steel microjoints fabricated using millisecond long Nd-YAG laser pulses was investigated experimentally and theoretically. The variables studied were pulse duration and power density. After welding, concentrations of iron, manganese, chromium, and nickel were determined at various locations of the microjoint using the electron microprobe analysis. The temperature field was simulated as a function of time from a well-tested three-dimensional transient heat transfer and fluid flow model. Using the computed temperature fields, vaporization rates of various alloying elements resulting from both concentration and pressure driven transport of vapors and the resultant composition change of the alloy were calculated. The calculations showed that the vaporization took place mainly from a small region near the center of the beam-workpiece interaction zone, where the temperatures were very high. Furthermore, the alloying element vaporization was most pronounced toward the end of the pulse. After the laser spot welding, the concentrations of manganese and chromium in the weld pool decreased, whereas the concentrations of iron and nickel increased. The composition changes predicted by the model were in fair agreement with the corresponding experimental results for various conditions of microjoining with short duration pulses.

A Study on Characteristics of Injection and Development of High Pressure Hydrogen Jet

In this paper, characteristics of injection and developing process of high pressure hydrogen jets were investigated using a constant-volume vessel. As an injection rate profile of a hydrogen jet, injected using an electronically-controlled, hydraulically-actuated gas fuel injector, is significantly related to jet penetrating and dispersing processes, the impact force of the jet was measured. And developing processes of high pressure hydrogen jets were visualized by means of shadowgraph photography to measure jet penetration, dispersion angle, volume, and pseudo equivalence ratio, Moreover, jet penetration profiles were approximated by the momentum theory in consideration of underexpanded jet flows. The results from injection rate measurements show that the injection rates during steady state portion of the injection are proportional to injection pressures and cross-sectional areas of the nozzle orifices. Regarding jet developing processes, the results represent the effects of injection pressure, orifice diameter, and ambient gas density on the jet penetration, dispersion angle, and entrainment. And the jet penetration predicted by the modified momentum theory was in reasonable agreement with the experimental results for various conditions of injection pressure, ambient density, and orifice diameter.

A thin 4pibeta-counter operating by negative high voltage for the 4pibeta-gamma coincidence measurement.-Construction.

A thin 4pibeta-multiwire proportional counter was constructed to increase the gamma-ray counting efficiency in the 4pibeta-gamma coincidence method. This counter with a counting volume of 70 X 60 X 11 mm and 5 wires in one half was made of an insulator and negative high voltage was supplied to the inner wall being possessed of conductivity. Then the anodes were operated at the earth potential and compact preamplifiers with no coupling condenser were fixed at the side of each half to miniaturize a shielding system for background. From the experimental results in various conditions, good characteristics were obtained in the case that signals were taken out from the center anode and the others were used only for cleaning up excess charges.

On Pulsation of Delivery Pressure of Gear Pump : In the Case of a Long Delivery Pipeline

In this paper, the authors deal with the pressure pulsations in a long delivery pipeline in consideration of the dynamic characteristics of the pipeline systems. The instantaneous parabolic delivery of a gear pump has been indicated as the sum of sine waves by being expanded into a Fourier series. The response of the delivery pressure in the long pipeline for it has been derived considering the internal leakage of the gear pump. The experiments have been performed in various line-conditions and speeds of the gear pump. It is shown that the theoretical solutions are in good agreement with the experimental results in various conditions.